Mixing device

ABSTRACT

Apparatus for mixing a fluid with a flowing material is disclosed including a chamber having an inlet for connection to a circular inlet conduit and an outlet for connection to a circular outlet conduit, and a supply conduit for supplying the fluid to the chamber, the inlet having a cross-section which is substantially circular at one end and which continuously transforms to a substantially elongated cross-section at the other end, and the outlet has a cross-section which is substantially circular at one end and which continuously transforms to a substantially elongated cross-section at the other end, and the supply conduit is located between the inlet and the outlet.

FIELD OF THE INVENTION

The present invention relates to a device for admixing an agent in theform of gas or liquid to a flowing material. More particularly, thepresent invention relates to a device comprising a chamber with an inletportion and an outlet portion to be connected to an inlet from a pipeand to an outlet from a pipe, each with a substantially circularcross-section. Still more particularly, the present invention comprisessuch a device with means for the supply of an agent to the chamber, andin which the material flow passes through the chamber whilesimultaneously the agent is supplied thereto.

BACKGROUND OF THE INVENTION

During the processing of pulp suspensions, various processing agents arerequired to be admixed therewith, for example for heating or bleachingpurposes. It is thus desired to disintegrate the agent in the pulp whilethe pulp is simultaneously transported through a pipe. For heating thepulp, steam is supplied, which condenses and thus emits its energycontent to the pulp. During bleaching a bleaching agent is supplied,which reacts with the pulp. In connection with the processing ofrecycled fiber pulp printing ink is separated by means of flotation,which requires that air shall first be disintegrated in the pulp.

In all of these cases, it is difficult to achieve a uniform admixture ofthe agent to the material flow with low energy addition. During theheating of the pulp by steam supplied to a pulp pipe problems oftenarise because large steam bubbles develop on the inside of the pipe.When these steam bubbles rapidly condense, condensate bangs areproduced, which cause detrimental cavitation in the pipe and downstreamequipment. This restricts the amount of steam which can be supplied tothe system, and the desired increase in temperature. It is alsodifficult to obtain an entirely uniform temperature profile in the pulp.For overcoming these problems, a large amount of energy can be suppliedin order to thoroughly admix the steam with the pulp. Another variant isto disintegrate the steam at the point of its supply to the pulp orprior thereto. During admixing of a bleaching agent with the pulp,relatively large amounts of energy are used in order to ensure that thebleaching agent is disintegrated and transported to all of the fibers inthe pulp suspension. The energy demand is controlled by the bleachingagent to be supplied (reaction speed) and by the phase of the bleachingagent (liquid or gas). The geometry during the supply of bleaching agentin the gas phase is important in order to avoid undesired separationdirectly after the admixture. Previous solutions of mixing deviceswithout movable parts have had a limited field of application due totheir geometric design and their low mixing efficiency.

One object of the present invention is a novel geometric design to solvethe problems with high energy addition, poor distribution of agent, andto avoid the risk of plug formation at the through-flow of pulpsuspensions.

The present invention is thus based on the following criteria.

Mixing is transport. The agent can be added at a point where there is along transport distance to the most remote fibers. This means that alarge amount of energy must be supplied for transport to all of thefibers. The agent can be added at one or many points with shorttransport distance to all of the fibers. This means that low or noenergy is required for transport to all of the fibers.

A pulp suspension in the higher concentration range, e.g., from 8% to18%, cannot be subjected to compression without risk of plug formation.This means high requirements on the geometric configuration of thedevice.

SUMMARY OF THE INVENTION

In accordance with the present invention these and other objects havenow been realized by the discovery of apparatus for admixing a fluidwith a flowing material comprising a chamber including an inlet portionfor connection to a substantially circular inlet conduit and an outletportion for connection to a substantially circular outlet conduit, andsupply means for supplying the fluid to the chamber, the inlet portionhaving a first end for connection to the substantially circular inletconduit and a second end, and the outlet portion having a first end forconnection to the substantially circular outlet conduit and a secondend, the inlet portion having a cross-section which is substantiallycircular at the first end and which continuously transforms to asubstantially elongated cross-section at the second end, the outletportion having a cross-section which is substantially circular at thefirst end and which continuously transforms to a substantially elongatedcross-section at the second end, and wherein the supply means is locatedbetween the inlet portion and the outlet portion. Preferably, the fluidcomprises a gas or a liquid.

In accordance with one embodiment of the apparatus of the presentinvention, the inlet portion and the outlet portion have a substantiallyconstant area from the first end to the second end thereof.

In accordance with another embodiment of the apparatus of the presentinvention, the apparatus includes throttle means disposed in the chamberbetween the inlet portion and the outlet portion. Preferably, thethrottle means creates a turbulent zone in the chamber, and the supplymeans is disposed at the beginning of the turbulent zone. In anotherembodiment, the supply means is disposed at the throttle means.

In yet another embodiment, the supply means is disposed prior to thethrottle means in a direction towards the inlet conduit. In yet anotherembodiment, the supply means is disposed subsequent to the throttlemeans in a direction towards the outlet conduit.

According to the present invention, a chamber is provided in a pipe witha substantially circular cross-section for the flow of material. Thechamber has an inlet portion, the cross-section of which successivelytransforms from circular to oblong, with a substantially maintainedarea, and an outlet portion, the cross-section of which successivelytransforms from oblong to circular, also preferably with a substantiallymaintained area. About the chamber between the inlet portion and theoutlet portion means for the supply of agent are connected.

According to a preferred embodiment of the present invention, thecentral portion of the chamber, between the inlet portion and outletportion, is formed with parallel opposed walls, which are united withrounded wall portions. Alternatively, the cross-section of the centralportion of the chamber can be elliptical, or it can have some otheroblong design.

The transformation from circular to oblong cross-section and from oblongto circular cross-section, respectively, should take place through acertain distance in the direction of flow. The minimum length of thisdistance is determined by the purpose of the application and theproperties of the material flow. The area of the oblong cross-sectioncan be defined for a rectangular shape as the product of height timeswidth. The minimum height of the oblong cross-section is determined bythe properties of the flowing material.

The chamber can be completed with a densitary throttle between the inletportion and outlet portion. Means for the supply of agent can be placedin the narrowest section, which renders the shortest transport distancebetween the point of addition of the admixed agent and all of theconstituents of the flowing material. The addition can take place in thethrottling, before the throttling or directly after the throttling.

The material flow passing through the chamber is supplied through aningoing pipe and is removed through an outgoing pipe. As a result, thegeometric change of the cross-section from circular to oblong takesplace without any change of area, or with a limited change of area, andthe material flow is not subjected to any substantial compression.According to the present invention, only a deformation of the flow fieldof the material flow takes place.

According to current theories for pipe flow, the flow rate at the pipewall is zero. These theories imply that there arises a rate gradientover the cross-section of the pipe. When this rate gradient reaches acertain size, the pipe flow transforms from a laminar state to aturbulent state in viscous materials. According to the presentinvention, this phenomenon is utilized in that the minimum height of theoblong cross-section is determined so that transformation from a laminarstate to a turbulent state for the definite material takes place. Byplacing a densitary throttling in the chamber, the material flow canadditionally be affected, and alternatively the throttling effect can beutilized for making the mixing device smaller. By creating the geometryso that transformation from a laminar state to a turbulent state takesplace, an efficient admixing of the agent is obtained when the agent isadded in the turbulent zone.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in greater detail in the followingdetailed description which, in turn, refers to the accompanying Figuresillustrating different embodiments of the invention, in which:

FIG. 1 is a side, perspective view of one embodiment of the deviceaccording to the present invention;

FIG. 2 is a front, elevational view of one embodiment of the deviceshown in FIG. 1, taken along section A—A thereof; and

FIG. 3 is a front, elevational view of another embodiment of the deviceshown in FIG. 1, taken along section A—A thereof.

DETAILED DESCRIPTION

FIG. 1 shows a chamber 1, which is connected to an ingoing pipe 2 and anoutgoing pipe 3 for a flow of material. These pipes, 2 and 3, havecircular cross-sections and are connected to an inlet portion 4 and anoutlet portion 5 of the chamber 1. The inlet portion 4 has across-section, which successively transforms from circular to oblong,with a substantially maintained or constant area, and the outlet portion5 has a cross-section which successively transforms from oblong tocircular with substantially maintained or constant area, as measured inthe direction of flow.

According to the embodiment of the present invention shown in thedrawings, the inlet portion 4 transcends directly into the outletportion 5, but the chamber can alternatively have a certain length witha uniform oblong cross-section between the inlet portion and outletportion.

In the transition from the inlet portion 4 to the outlet portion 5 means6 for the supply of processing agent are connected all around thechamber 1. These means 6 can suitably consist of a plurality of nozzles,which are uniformly distributed about the periphery of the chamber 1. Asmentioned above, admixing of the agent is promoted by the deformation ofthe material flow caused by the geometric change of the cross-section inchamber 1.

FIGS. 2 and 3 show by way of cross-section taken along section A—A inFIG. 1 two embodiments, one embodiment (FIG. 2) without densitarythrottling in the chamber 1, and a second embodiment (FIG. 3) with adensitary throttling 7 placed in the chamber 1 between the inlet portion4 and outlet portion 5. Means 6 for the supply of agent are formed asnozzles or oblong slits (not shown in the Figures) directly in the wallof the chamber 1 or in the throttling 7. Alternatively, the means 6 canbe placed directly before or after the throttling 7. The throttling 7creates shear stresses of short duration arise in the material flowthrough the chamber, which in certain cases can promote the admixing ofthe agent even more. According to a preferred embodiment of the presentinvention, the means 6 are placed at the beginning of the turbulent zoneformed by the throttling. The means 6 consist of small circular holeswith their outlets directed to the material flow.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

1. Apparatus for admixing a fluid with a flowing material comprising achamber including an inlet portion for connection to a substantiallycircular inlet conduit and an outlet portion for connection to asubstantially circular outlet conduit, and supply means for supplyingsaid fluid to said chamber, said inlet portion having a first end forconnection to said substantially circular inlet conduit and a secondend, and said outlet portion having a first end for connection to saidsubstantially circular outlet conduit and a second end, said inletportion having a cross-section which is substantially circular at saidfirst end and which continuously transforms to a substantially elongatedcross-section at said second end, said outlet portion having across-section which is substantially circular at said first end andwhich continuously transforms to a substantially elongated cross-sectionat said second end, and wherein said supply means is located betweensaid inlet portion and said outlet portion.
 2. The apparatus of claim 1wherein said fluid comprises a gas or a liquid.
 3. The apparatus ofclaim 1 wherein said inlet portion and said outlet portion have asubstantially constant area from said first end to said second endthereof.
 4. The apparatus of claim 1 including throttle means disposedin said chamber between said inlet portion and said outlet portion. 5.The apparatus of claim 4 wherein said throttle means creates a turbulentzone in said chamber, and wherein said supply means is disposed at thebeginning of said turbulent zone.
 6. The apparatus of claim 4 whereinsaid supply means is disposed at said throttle means.
 7. The apparatusof claim 4 wherein said supply means is disposed prior to said throttlemeans in a direction towards said inlet conduit.
 8. The apparatus ofclaim 4 wherein said supply means is disposed subsequent to saidthrottle means in a direction towards said outlet conduit.